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AUTOMATED SYSTEMS
1st lesson 4 ELT A
Linear systems
Multimedia technicians Lorenzo
Bianchini Paolo G. De Maio
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• Automated processes
• are regulated by time
• but, as you know
• sometimes we will work
• inside frequency domain

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• System theory

• The birth of a mathematical theory capable of
  analyzing complex systems allowed the field of
  research to be extended to natural systems
• Biological systems
• Economic systems
• Physics sistems
• Social systems

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• What is a system?

A portion of reality whose behavior can be
described by the evolution along the time of a
set of variable quantities (called output) as a
function of a set quantities that can be modified
from the outside (called input)
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• From 1st year lessons the following definitions
  are evolved as follows

System a combination of components that act
together to perform a function not possible with
any individual parts. The word System is
interpreted to include physical, biological,
organizational, and other entities which can be
represented through a common mathematical
symbolism. The formal name system engineering can
also be assigned to this definition of the word
System. Thus, the study of feedback control
systems is essentially a study of an important
aspect of systems engineering and its application.
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• Static and dynamic systems

A system is static if the outputs depend only
on the inputs of the same instant. A system is
dynamic if the outputs depends not only on the
inputs in that very instant, but also on the past
inputs, meaning the system has a memory whose
description is given by a set of variables called
state
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• The art of automatic control systems permeates
  life in all advanced societies today.
• Such systems act as a catalyst in promoting
  progress and development.

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One of the earliest automated systems was Heros
devices for opening the doors of a Temple, the
command input was lighting a fire upon the altar
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The devices was probably actuated when the Ruler
and his entourage started to ascend the Temple
steps, and so time was a fundamental variable to
calculate obviously we can consider it an open
loop system.
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Systems in which the output quantity has no
effect upon the input quantity are called Open
loop control system
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For example, we go to a banquet in, say, 100 BC.
A bowl of wine sits on a center table with a
spigot above it. The guests dip wine from the
bowl. As the level drops, wine magically begins
flowing from the spigot to refill the bowl.
  Inside, hidden from view, is a ball-and-cock
float-valve, just like the one in your toilet.
It's pure feedback control. It senses, compares,
and corrects the liquid level by itself, without
human intervention.
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That sort of thing was common in the Hellenistic
world. One of the first feedback devices was
the water-clock flow regulator. The 3rd-century
BC engineer Ktsebios made the ancient water-clock
into an accurate timekeeper by inventing a float
stopper to regulate a constant flow of water into
the indicator tank.
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Experience of some ancient Hellenistic engineers
bore its fruit after 1800 years. The feedback
concept was right at the heart of 18th-century
revolution (not only industrial). The concept of
self-correction is what democracy is all about.
Think about this
The concept of self-correction is what democracy
is all about.
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Closed loop implies that the action resulting
from the comparison between the output quantities
and input quantities acts in order to maintain
the output at the desired value
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James Watts flyball governor for controlling
speed, developed in 1788, can be considered the
first feedback control system not involving human
being.
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Watt's governor was a superb example of feedback
control. Feedback controllers, mechanisms that
sense a discrepancy and correct it, are
absolutely shot through our world today. We go
through hardly an hour of any day without using
feedback devices float valves in our toilets,
thermostats in our rooms, pressure-control valves
and carburetion electronics in our cars etc..
Water mills flow governor
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As you know, the desired performance
characteristic of a system, may be specified, for
example, in terms of the transient response to a
unit step-function input.
Last year, we studied basic mathematical tools to
analyze systems in time domain (state matrices)
and in frequency, or better, complex variable s
(Laplace transform).
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Industrial- process temperature- control system
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Industrial- process temperature- control system
Ref
e
Temp
Temp
G
G


-
-
H
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Industrial- process temperature- control system
G
H
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• In general terms
• Open loop
• Faster
• requires perfect knowledge about the system
• Closed loop
• Slower
• can deal with a wide class of problems

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In the next two years, while deepening the study
of control systems in analog domain, well
discover that the two previous sentences are not
completely true. The closed loop can cause
problems of system instability. We will spend
many lessons in analyzing these phenomena in
Time or Frequency domain.
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